Geology for dummies err climbers

[Jake_Gano]

Ok I know nothing about geology and since about 90% of the climbing I do is on granite I haven't really had the chance to learn much about the rocks we climb. Is there any good Geology 101 sites out there written specifically for rock climbers?

[iain]

The USGS has things like this:

http://wrgis.wr.usgs.gov/docs/parks/noca/nocaft.html

 

and this:

http://wrgis.wr.usgs.gov/docs/parks/noca/nocageol1.html

 

dunno if that's a help. It would help to know what kind of geology you are interested in: petrology, stratigraphy/seds, structural geology, geochemistry, etc. for instance you can talk about the chemical composition of rocks on Rainier, or the flow structure in its debris.

[Alasdair]

Ok I know nothing about geology and since about 90% of the climbing I do is on granite I haven't really had the chance to learn much about the rocks we climb. Is there any good Geology 101 sites out there written specifically for rock climbers?

I suggest you read Cascade alpine guides. Fred Clearly has a pretty good grasp on geology and those books have a lot of basic info in them. Ah and Granite is Granitorite but granitorite is not granite. Most granitic rocks in the northwest are not granite, but most climbers just assume they are. Granite has bigger ofter pink crystals.

[Dru]

Granitorite?????

 

There are four types of rocks

sedimentary (sandstone limestone etc)

igneous intrusive (granite, granodiorite, monzonite, gabbro, dunite etc)

igneous extrusive (basalt, andesite, ryolite, tuff etc)

metamorphic (gneiss, quartzite, shale, schist etc)

 

Sedimentary rocks are sediment (dirt and/or sea floor ooze) that has been hardened and solidified into stone

Igneous intrusives are lava that cooled sl;owly below the ground

Igneous extrusives are lava that cooled quickly at the surface (plus ash and so on which isnt really lava)

Metamorphic rocks are sedimentary or igneous rocks that got altered through heat, pressure and burial over the course of geologic time.

 

There are good and bad rocks to climb on of every type.

 

The Audobon Field Guide to Rocks and minerals is a good book for the non-geologist that will also help you look for gold and gems while bushwacking up a creek bed.

[willstrickland]

Dru, what are some of the parent/resultant relationships in metamorphics beyond the basics? Also, isn't shale sedimentary from mud?

 

I know that:

 

Sandstone->quartzite

granitics->gneiss

shale->slate

 

But schist can form from basalt, shale, or slate?

 

Others?

[Dru]

Low grade metamorphism will make gneiss from granite or volcanic rocks, schist shale or slate from mudstone and sandstone and volcanic rocks, marble from limestone etc. If you cook it enough basically anything but a pure quartz sandstone or a limestone will end up becoming a gneiss. This is why all the oldest rocks in the world end up as gneisses.

 

Basically though, none of this is relevant for climbing. All you need to know is that most igneous intrusive rocks ("granites" even though chemically granite is not all that common) are pretty good to climb on, limestone can be good or bad, basalt is often pretty good, sandstone varies from good to bad and everything else sucks! Also you dont get many good cracks except in granites, sandstone and basalt.

[kurthicks]

Jake,

just take Geology 101 at school. it's an easy A and a science credit.

[iain]

Some knowledge of structural geology will keep you off desperate down-sloping holds and underclings. Trapse across some of the faces on Mt. Sir Donald for some examples.

[klenke]

Jake needs to take the class just so he can spell the rock types correctly.

It's granodiorite.

Incidentally, according to one of my NW geology books. The Golden Horn Batholith near Rainy Pass is the only true granite in the state (peaks such as Golden Horn & Tower Mountain). All other granites in the state are granodiorites. Albeit, "granite" is a catch-all word used to denote pure granite, granodiorite, quartz diorite, and diorite. Independent diorite is rare; granodiorite is common.

[Dru]

"granite" also includes monzonite and quartz monzonite smart guy

 

Diorite is pretty common. I have a lump of it across the street from me I can look at as I type.

[klenke]

Hmm, I've read some sources that say stand-alone diorite is rare. It's usually bound in with other minerals, such as (pure) granite and quartz, or so I thought.

 

Thanks for the monzonite addition. I'm not a geologist so can't be counted on to remember everything.

 

--smart guy

[Dru]

granite is not a mineral. neither is diorite.

 

the differences between granite, granodiorite, monzonite, quartz diorite, diorite, nepheline syenite, gabbro and dunite are chemical - the relative composition of the minerals making up the rock. quartz, three types of feldspar, mica, honblende and amphibolite usually. so granite has a lot of quartz and sodic feldspar, then as you go across the spectrum the feldspar changes with ratio of sodic to calcic and then potassium feldspar, and as you move into granodiorite and diorite you tend to lose the quartz altogether, then gabbro has almost no feldspar but is mostly mica, hornblende, amphibolite and other mafic rocks, finally you get dunite which is 100% olivine like the Twin Sisters.

 

Chemically the light-coloured granites are equal to the light-coloured lavas like rhyolite and dacite that form volcanic ash... diorite and gabbro are equivalent to andesite and basalt... take Geol 100 to find out why.

[klenke]

I'm not going to call a full bullshit on you but you do need to look up the word mineral in the dictionary. As I recall, you and I had this discussion on semantics about a year ago in a similar thread.

 

I'm going to stick with granite and quartz being a mineral, "a solid homogenous crystalline chemical element or compound that results from the inorganic processs of nature." Everything you listed above is a mineral, a chemical variation of a theme.

 

[iain]

granite is not a mineral. quartz is, however.

 

diorite can be quite common. It is basically granite with less potassium feldspar, the pink stuff. It is much more "black and white" in appearance, though that is not a definitive description.

 

so does monzonite ever have monazite in it? gawd I'm glad I'm not studying this stuff anymore.

[iain]

haha you guys are posting way to fast for me now I look like an idiot! (par for the course, I suppose)

[klenke]

Tell me why granite is not a mineral. Then tell me why quartz is.

[iain]

To repeat, granite is most definitely not a mineral. It has a bunch of quartz in it.

[iain]

Tell me why granite is not a mineral. Then tell me why quartz is.

 

Because granite is a mixture of many other minerals, such as feldspar and quartz. It is formed through relatively slow cooling, hence the large crystals it typically has. It is the same as rhyolite (as dru said), but rather than cooling quickly, it has cooled slowly, usually at depth.

[iain]

as for quartz, it has a definite crystal structure, a uniform hardness, a uniform chemical composition, etc. It's a mineral by these definitions. It is one of the primary minerals in granite, however.

[klenke]

Why should it matter what it's made of that determines if granite is a mineral or not? A mineral is a chemical compound. Granite is a chemical compound--an amalgam of various other chemical compounds.

 

If granite is not a mineral, what is it?

 

From a book of mine called "Minerals Encyclopaedia" (1999, Korbel & Novak):

"There are minerals known to humankind since prehistoric times such as quartz and gold." If a pure element like gold or copper can be considered a mineral, then why not granite.

 

Here's a mineral for Dru out of the above book:

Dickite Al2-Si2-O5(OH)4

Monoclinic -- uncommon -- other info I'll omit here.

[Dru]

Yeah, granite is a rock, not a mineral. A rock is made out of minerals like a cake is made out of raisins, sugar and flour. There is really no rock called quartz, except I suppose you could call hydrothermal deposits and veins quartz rock as they are 100 quartz crystals. There are pure quartz crystals (Silicon Dioxide Si02), and quartzite rock, which is a type of rock made of grains and pebbles and so on quartz. Also you get chert which is a hydrated amorphous Si02... blah blah!

[iain]

If granite is not a mineral, what is it?

 

Granite is what's known as a rock!

[klenke]

So granite is a mixture?

[Dru]

Granite is not "a chemical compound". It is an assemblage of minerals. Just like a molecule is not an atom.

[klenke]

So granite in general is a mixture, I understand that. But once you get down to one chunk of granite with a definite chemical constituency, that chunk (if homogenous) is a mineral. That is, you can write out a chemical formula for it.